India is on track for another bad year of H1N1 or swine flu infections, recording more than 19,000 cases and more than 600 deaths since the beginning of the year. The worst outbreaks of this respiratory illness have occurred in the swine flu hotspots in western India – Rajasthan, Maharashtra and Gujarat – as well as in Delhi, Haryana, Karnataka and Telangana.

Since 2009, when H1N1 caused a global pandemic, strains of the virus have been circulating in India, which has recorded a few hundred infections in some years and many thousands in others. The worst years in terms of the number of cases and deaths have been 2015, 2017 and now possibly 2019.

But India also has circulating strains of influenza B and H3N2, both of which cause infections, hospitalisation and death. But because it does not conduct countrywide surveillance for other types of influenza, cases of influenza B and H3N2 are not as carefully reported as cases of H1N1, say researchers, who also believe that H1N1 cases may be undercounted. They say more data on the various strains of influenza detected in India will lead to better vaccines being developed.

Pattern of infection

The number of people infected with the swine flu virus is closely linked with the pattern of infection, explain virologists.

The influenza virus has important surface cells proteins called antigens. When the human body encounters the virus either through vaccination or infection, the immune system identifies the antigens and produces antibodies to fight the infection. The antibodies that remain in the body also fight off any subsequent infection by the same virus with the same antigen. But influenza viruses often find a way around.

“The influenza virus is tricky and often its RNA undergoes small variations, which results in small changes in the surface proteins, which may not be recognised by the antibodies already created,” said Dr Abhay Chowdhary, professor and head of microbiology at DY Patil University in Mumbai and former director of the Haffkine Institute that is a part of the government’s influenza surveillance network. “The virus is then again able to cause infection in the same people. This again causes an outbreak with larger number of people being infected till the population once again builds immunity to the slightly changed virus.”

This is what seems to have happened in India between 2015 and 2017 and once again between 2017 and 2019.

“At the beginning of 2017, a lot of people got infections and may have been symptomatic or asymptomatic but would have developed immunity,” said G Arunkumar, professor and head of the department of virus research at Manipal Centre for Virus Research. “In 2018, there were not many infections and by about September the virus has slightly changed and the people who had developed immunity earlier would have become susceptible once again.”

* The figures for 2019 are as of March 10.

Sajjan Shetty, joint director of the National Vector Borne Disease Control Programme in Karnataka, also noted that there were very few H1N1 cases from January 2018 to September 2018. “From October, there was a rise in cases in western India – Rajasthan, Maharashtra and Gujarat and then Karnataka,” he said. “In December and January there was a slight decline and in February the number of cases began to rise again.”

Influenza outbreaks are not very predictable but the pattern that has emerged in India is a spike in cases in the monsoon months.

This year there could be a peak in the number of infections in May that will continue into the monsoon, predicted Arunkumar. But he expects H1N1 activity to fall after July.

The number of infections is largely due to the changing nature of the influenza virus from time to time, but the number of deaths during an outbreak is linked to the lack of vaccination and to delayed treatment.

The H1N1 slant

Arunkumar said that a different influenza virus may be dominant every year and during different periods of a given year, but the health surveillance system was skewed towards H1N1.

“Last year, the number of people who had H1N1 and the number who were admitted to hospital with influenza B were nearly the same, but that was not noticed because countrywide surveillance for other types of influenza is not done,” said Arunkumar. “Throughout the year, we see one of the other type of influenza but our systems only get activated if we see H1N1 cases. Other types of influenza also result in hospitalisation and cause death.”

Said Shetty: “The majority of influenza cases are actually that of influenza B.”

The number of influenza cases in India may be much higher than what is reported and there are probably many more H1N1 cases too, say experts, because of the treatment protocol that is followed when someone is suspected of having contracted influenza.

The drug to treat influenza A (including H1N1) and influenza B is oseltamivir, better known by its brand name Tamiflu. The drug is effective only if administered at an early stage of the illness, preferably within 24 hours of the onset of symptoms. Health authorities have therefore issued guidelines to doctors not to wait for a person to be tested and confirmed as H1N1 positive but treat anyone with clinical symptoms of the disease with the drug. Delayed treatment can lead to escalation of symptoms that can be fatal.

“Only C-category patients who have fever breathlessness and blood in the sputum are tested,” said Shetty. “Many others with milder symptoms are given Tamiflu and sent home to recover.”

Shetty also said that often influenza B and H3N2 may also be reported as H1N1. “The symptoms are similar, treatment is the same so there is not much benefit from making the distinction.” he added.

But better surveillance and reporting of all types of influenza will help in creating better vaccines.

The vaccine

Every year, the World Health Organisation takes stock of the circulating strains of influenza and recommends flu vaccines, one for the northern hemisphere and one for the southern hemisphere.

This year, it has recommended for the Northern Hemisphere a quadrivalent vaccine that contains strains of H1N1, H3N2 and two strains of influenza B. For H1N1 it had recommended using the Brisbane strain of the vaccine, unlike in 2017 and 2018 when it recommended the Michigan strain.

The Michigan strain and the California strain of H1N1 are known to circulate in India.

An isolation ward for swine flu patients at Coronation hospital in Dehradun, Uttarakhand. (Photo credit: IANS).

“If we strengthen our surveillance, a strain that is more appropriate for India may also get into the vaccine,” said Arunkumar. “We need state-specific and regional-specific data and the viruses should be analysed. The National Institute of Virology is doing it but given the large population in India, our contribution do influenza strain identification should be much more. You see countries like China and Thailand contributing a lot to the influenza database.”

The World Health Organisation and the health ministry recommend vaccination for health workers who are at higher risk of exposure to influenza and also for people with existing medical conditions – also known as co-morbid conditions – such as respiratory disease, heart disease, liver and kidney disorders and cancer, which make them more susceptible to infection and more at risk of death due to infections. They also recommend vaccination for people above the age of 65 and children younger than eight.

However, in many parts of the country, flu vaccination is only given to health workers. “We have constituted a committee to look into the recommendation of giving vaccination against influenza,” said Dr Ravi Prakash Sharma, additional director for rural health in Rajasthan. “Right now, we are only giving it to health workers who might be at risk by coming into contact with people with swine flu.”

In Rajasthan, 162 people have died this year of which about 70% had co-morbid conditions, according to Sharma.

Shetty said that Karnataka also was administering the vaccine only to at-risk health workers like doctors and nurses in out-patient departments. Both government officials said that even though the public health system was not offering the vaccine to anyone else, it was available in the market.